1. Field of the Invention
The present invention relates to an organic-inorganic nano composite comprising a styrene-butadiene copolymer, an acryl-based monomer, a living radical polymerization initiator, silica, and a coupling agent. The organic-inorganic nano composite is prepared using a method comprising: preparing a spherical styrene-butadiene copolymer; preparing a nano-sized spherical styrene-butadiene-acrylate copolymer using living radical polymerization of the spherical styrene-butadiene copolymer and an acryl-based monomer; and preparing a composite by coupling the nano-sized spherical styrene-butadiene-acrylate copolymer and silica.
2. Background Art
Typically, styrene-butadiene copolymers or styrene-butadiene-acrylate copolymers are prepared using emulsion copolymerization. These copolymers are used for tires, coating materials, toners, or the like. Various methods of preparing styrene-butadiene copolymers or styrene-butadiene-acrylate copolymers by emulsion copolymerization have been reported. For example, U.S. Pat. Nos. 3,575,913 and 3,563,946 disclose a styrene-butadiene or styrene-butadiene-acrylate copolymer prepared by emulsion polymerization using potassium persulfate or azobis iso-butyronitrile. U.S. Pat. No. 4,064,081 discloses a method of preparing a butadiene-styrene-itaconic acid copolymer by emulsion polymerization using potassium persulfate as a polymerization initiator. U.S. Pat. Nos. 5,274,027 and 5,302,655 disclose methods of preparing a styrene-butadiene-acrylate copolymer by emulsion polymerization using itaconic acid and methyl methacrylate as acrylate-based compounds and ammonium persulfate as an initiator are used. In addition, U.S. Pat. Nos. 5,395,891 and 6,127,488 disclose methods of preparing cross-linked polybutadiene or styrene-butadiene copolymer by emulsion polymerization for an organic filler. However, the organic filler has low tan δ and abrasion resistance.
In addition, U.S. Pat. No. 6,780,937 discloses a composite comprising 25 wt. % of a diene unit, at least 70 wt. % of an aromatic vinyl compound, and 0.1-30 wt. % of a functionalized monomer unit. Even though the composite has a glass transition temperature of 150° C. or higher and excellent wet traction capability due to a high hysteresis at a low temperature, it has too high hardness and modulus.
In the styrene-butadiene copolymers or styrene-butadiene-acrylate copolymers prepared by conventional emulsion polymerization, the distance between particles is decreased due to reactions by radicals, and the degree of cross-linkage is increased within particles. Furthermore, it is difficult to coat silica on the particles or to prepare nano composites. In particular, it is difficult to prepare nano-sized spherical copolymers and silica nano composites.
Thus, there is still a need for the development of a novel composite to be used in the manufacture of conventional tires to improve their properties.